\begin{tikzpicture}[>=Stealth,
    every node/.style={fill=white, inner sep=1pt},
]
    \pgfmathsetmacro{\a}{3.2}
    \pgfmathsetmacro{\b}{2}
    \pgfmathsetmacro{\c}{0.2}

    \pgfmathsetmacro{\x}{0.8}
    \pgfmathsetmacro{\y}{1.0}

    \draw [ultra thick, pattern={mylines[angle=45, distance={5pt}]}] (0, 0) rectangle (\a, \b);

    \draw [ultra thick, fill=white] (0, 0) rectangle (\x, \y);
    \draw [ultra thick, fill=white] (\x + \c, 0) rectangle (\a, \y);
    \draw [ultra thick, fill=white] (0, \y + \c) rectangle (\x, \b);
    \draw [ultra thick, fill=white] (\x + \c, \y + \c) rectangle (\a, \b);

    \draw [<->] (0, -0.3) to [xianduan={above=0.3cm}] node {$32 \; cm$} (\a, -0.3);
    \draw [<->] (-0.3, 0) to [xianduan={below=0.3cm}]  node [rotate=90] {$20 \; cm$} (-0.3, \b);
\end{tikzpicture}

